Conventionally, in word processors, personal computers, portable TVs, and the like, thin and lightweight flat display devices are widely used. Among them, in an active-matrix type liquid crystal display device, a thin film transistor (TFT) is disposed at each intersection between a plurality of signal lines and a plurality of scanning lines. This liquid crystal display device has the advantage of being excellent in chromogenic characteristics and having fewer afterimages.
Progress in the manufacturing process technology in recent years allows driver circuits to be integrally formed on an array substrate, thus the number of connection parts and of connecting wires with the outside are reduced. As a result, cost reduction can be achieved. Then, there is known a technique described in Japanese Patent Application Laid-Open Publication No. 2001-312255, for example. This technique allows to correspond a video signal line from a driver IC with signal lines on an array substrate by 1:N (N is an integer equal to or greater than 2) in a liquid crystal display device, thereby enabling a multi-selection drive in which one signal line is sequentially selected out of a group of N signal lines in one horizontal scanning period by an analog switch circuit and then the selected one is connected to a video signal line.
Generally, methods of writing a video signal from a signal line to a pixel include a vertical line inversion driving method and an H/V inversion driving method (also called a dot inversion drive). In the vertical line inversion driving method, the polarity of a signal line is inverted between adjacent signal lines to provide a video signal. In the H/V inversion driving method, the polarity of a signal line is switched for each horizontal scanning period to provide a video signal, and at the same time, the polarity of a signal line between adjacent signal lines is inverted to provide a video signal.
For example, in a 2H2V inversion driving method of selecting four signal lines, in which the value of N in the multi-selection drive of signal lines is set to 4 and the polarity of a signal line is switched every two horizontal scanning periods to provide a video signal, and also the polarity of the adjacent signal lines is inverted every two signal lines to provide a video signal, a signal line is driven while providing a periodicity of every M scanning lines (M is an even number) to the voltage polarity of the signal line.
Recently, there is known a technique described in Japanese Patent Application Laid-Open Publication No. 2005-92176, for example. Taking into consideration the presence of polarity inversion of each signal line between adjacent scanning lines in a liquid crystal display device and the presence of polarity inversion between adjacent signal lines when selecting one signal line out of a group of N signal lines, this technique controls the selection order of signal lines to be selected earlier and the selection order of signal lines selected later in each group. This makes less visible the unevenness caused by write deficiency due to polarity inversion of a signal line.
Switching of the voltage polarity of signal lines with such periodicity is carried out for each frame. Specifically, this is carried out at the timing when a data enable signal indicating that a video data signal is to be provided from an external device has been identified for the first time at the beginning of a frame.